No longer any need to delete the line box tree on our own.

Source/core/layout/LayoutMultiColumnFlowThread.cpp

Index: Source/core/layout/LayoutMultiColumnFlowThread.cpp
diff --git a/Source/core/layout/LayoutMultiColumnFlowThread.cpp b/Source/core/layout/LayoutMultiColumnFlowThread.cpp
index 478f89d9d701fd067c66d0e799cfbdb7284497dc..7cc0c14770975a2ae3d149b00492a7dad984176b 100644
--- a/Source/core/layout/LayoutMultiColumnFlowThread.cpp
+++ b/Source/core/layout/LayoutMultiColumnFlowThread.cpp
@@ -255,11 +255,9 @@ void LayoutMultiColumnFlowThread::evacuateAndDestroy()
     multicolContainer->resetMultiColumnFlowThread();
     moveAllChildrenTo(multicolContainer, true);
 
-    // FIXME: it's scary that neither destroy() nor the move*Children* methods take care of this,
-    // and instead leave you with dangling root line box pointers. But since this is how it is done
-    // in other parts of the code that deal with reparenting layoutObjects, let's do the cleanup on our
-    // own here as well.
-    deleteLineBoxTree();
+    // We used to manually nuke the line box tree here, but that should happen automatically when
+    // moving children around (the code above).
+    ASSERT(!firstLineBox());
 
     destroy();
 }